Variable inductor



Feb. 10, 1959 R. E. MARSH 2,873,431

VARIABLE INDUCTOR Filed July 12, 1954 United States Patent 2,873,431 VARIABLE mnuc'ron Richard E. Marsh, Oak Park, 111., assignor to-The Hallicrafters Co., a corporation of Delaware Application July 12, 1954, Serial No. 442,872

, 2 Claims. (Cl. 336- 135) This invention relates to a variable inductor and more particularly to an inductor including a high permeability core structure having a variable air gap therein.

Recent developments in metallurgy have resulted in the availability of high permeability, low loss magnetic core materials such as ferrites, with which relative permeabilities of the order of one thousand and very low radio frequency losses are readily attainable. I have devised and disclose and claim herein a variable inductor utilizing such core material and which may have an inductance range of the order to -1, or greater.

One feature of my invention is that it provides a variable inductor including a first element, coil means operably associated therewith and a second core element, operably associated with the first, the core elements providing a flux path for the coil means and being adapted for relative movement therebetween effecting a variation in the inductance of the coil; Another feature of the invention is that movement between the core members changes the reluctance of the flux path of the coil, effecting a variation in the inductance thereof.

A further feature is that the core members are arranged so that an air gap is provided in the flux path of the coil, movement of one of the members changing the size of the air gap, varying the inductance of the coil. Yet another feature is that one of the core members has a portion on which the coil is wound.

Still a further feature is that the inductor comprises a first ferrite core segment having a raised center portion and a peripheral portion with a coil wound on the center portion, and a second core segment or ferrite cap ele ment movably mounted with respect to the first core segment, the core segments forming a flux path for said an having an air gap therein, movement of said second core segment with respect to the first varying the size of the air gap and causing variation in the inductance of the coil.

Further features and advantages of the invention will readily be apparent from the following specification and from the drawings, in which:

Figure l isa top plan view of the invention, with the core segments in half open position;

Figure 2 is a side elevational view of the inductor of Figure 1 with the core segments fully closed;

Figure 3 is a top plan view of the base core segment;

Figure 4 is a top plan view of the cap core segment;

Figure 5 is a vertical sectional view of the base core segment taken along the line 5-5 of Figure 3; and

Figure 6 is a vertical sectional view of the cap core segment taken along the lines 6-6 of Figure 4.

The use of materials having a high permeability, such as ferrites, as a core material for inductors is well known. Normally such inductors take the form of a coil wound around a tubular form of paper or ceramic with a rod or plug of core material inserted therein. The slug may be fixedly or movably mounted depending upon whether the inductor is to have a fixed or variable inductance.

2,873,431 Patented Feb. 10, 1959 With such variable inductors, an inductance range of up to 5-1 has been achieved. The variable inductor of this invention may have an inductance range of the order of 10-1 or greater.

In the drawings, reference numeral 10 indicates a first or base core element while reference numeral 11 indicates a. second or cap core element. These two core elements are preferably made for a ferrite material having a very high relative permeabilitibas of the order of at least 1000, and also having very low radio frequency. losses. The first and second core elements 10 and 11 both have the shape of a segment of a circle, and are slightly less than a semicircle in size.

As may best be seen in Figures 3 and 5, an arcuate channel 10a is cut in the case core element intermediate the center and periphery thereof, defining an upstanding center portion 10b and an upstanding arcuate peripheral portion 100. The coil 12 is wound about the center portion 10b which is preferably circular in cross-section- It should be noted that the center portion 10b is slightly higher than the peripheral portion 100.

As shown in Figure 2, a shaft 14 extends through an opening 10d in the center portion 10b of the first or base segment of the core. The cap segment 11 is provided with a similar opening 11a through the inner portion thereof by means of which it may be mounted on the shaft 14. The base segment 10 may be fixedly mounted and the shaft 14 adapted to rotate in the opening 10b. The cap segment 11 is securely afiixed to the shaft 14 as by a pin 15, or any other suitable means.

As pointed out, the center portion 10b of the base segment extends above the peripheral portion thereof. Accordingly, when the core segments are mounted on the shaft 14 and the cap segment 11 is brought into contact with the center portion 10b of the base segment, an air gap remains between the peripheral portion 100 of the base and the outer periphery of the cap segment 11. Except for this air gap, the core segments 10 and 11 form a closed low reluctance core for the coil 12, providing an inductor having a much greater inductance than that of the winding alone.

If the shaft 14 is rotated, the cap segment 11 will turn with it, as shown in Figure 1, and the area of the air gap between the core members will be varied. This in turn varies the reluctance of the core and accordingly effects a variation in the inductance of the coil 12.

The inductance variation may be made quite large even in excess of 101. Furthermore, this ratio is not dependent upon the absolute value of the inductance of the coil but rather on the physical characteristics and size of the core segments. By varying the shape and spacing of the core segments, many different relationships between the angular position of the cap 11 and the inductance of the coil may be provided.

One application which suggests itself for this variable inductor is in the tuning section of a superheterodyne radio receiver. As the variable inductor may have an inductance ratio of 10-1 or greater, it can be used to replace the relatively expensive variable tuning condensers which are commonly used for effecting tuning in radio receivers. A number of variable inductors may be ganged for simultaneous operation by mounting the movable segment of each inductor on a single shat While I have shown and described certain embodiments of my invention, it is to be understood that it is capable of many modifications. Changes therefore in the construction and arrangement may be made without departing from the spirit and scope of the invention as disclosed in the appended claims.

I claim:

1. A variable inductor of the character described, in-

c1uding: a first core segment comprising a base element having the shape of a sector of a circle, and being cut out to have an arcuate channel defining a cylindrical e er p r iq a a .p n l. Por n, t n er P9 tion being-slighflyhighenthan the-peripheral portion; a

coil wound on said cjlindrical center portion and filling said channel, the coil terminating below the top of said peripheral portion; and a sec ond core segment comprising a planar cap element having the shape of a sector-of a circle, said second segment being rotatably secnre'd to said first segment and fitting tightly against said center portion, there being a gap hetweensaidcap element and the rperipheral portion-of said base element, rotationof said cap efiecting a change in the inductance of said 2. A variable inductor as described inclaim 1, wherecircle in size.

References Cited in the file of this patent UNITED STATES PATENTS 1,234,280 Burnett July 24, 1917 2,090,991 Wohlfarth Aug. 24, 1937 2,107,172 Agricola- Feb. 1, 1938 2,341,345 Van Billiard Feb. 8, 1944 238939156 Keen Nov. 27, 1945 2,483,900 Hardeiilierg Oct. 4, 1949 "FoREiGfi PATENTS 425,468 GreafBiitaia Mar. 6, 1935 442,849 Great Britain Nov. 19, 1934 

